1. Field of the Invention
The present invention relates to a printing apparatus providing variable print impact pressure which thereby prevents nonuniform printing density caused by a difference between the areas of different typefaces.
2. Description of the Prior Art
U.S. Pat. No. 3,858,509 is an example of prior art in the field of printing apparatus of the type to which the subject invention relates.
The patent mentioned discloses a printing apparatus which provides only two different levels of type impact pressure and which cannot provide a sufficient range of the impact pressure for various typefaces. The two different levels of impact pressure are provided by two one-shot multivibrators. Therefore, in order to increase the number of levels of impact pressure, a larger number of one-shot multivibrators must be provided. As a result, the printing apparatus itself would become large and would be expensive to manufacture.